This invention relates to a carbide-dispersed type Fe-base sintered alloy which exhibits excellent wear resistance when used as a sliding part required to have high lubricity enough to be in smooth sliding contact with a counterpart, e.g. a sliding part in an internal combustion engine using liquefied petroleum gas (LPG) as fuel.
Carbide-dispersed type Fe-base sintered alloys as well as chilled castings are generally employed as sliding parts in internal combustion engines using liquefied petroleum gas (hereinafter abbreviated as LPG) as fuel, such as rocker arms and valve lifters. Such Fe-base sintered alloys have such a structure that carbides of Fe, Cr, and/or Mo are dispersed in the matrix, as disclosed, e.g. in Japanese Provisional Patent Publications (Kokai) Nos. 60-194048 and 61-60862.
However, sliding parts in internal combustion engines are placed under very severe operating conditions because LPG has so poor lubricity that no oil film can easily be present between the sliding parts and their counterparts. Under such severe operating conditions, conventional carbide-dispersed type Fe-base sintered alloys, like conventional chilled castings, are subject to metal adhesion with their counterparts, since the percetage of carbides dispersed in the matrix is about 60% by volume at most. In a worse case, sliding parts have scuffing wear of a depth of the order of 0.5 mm and often heavily damage or abrade surfaces of their counterparts (e.g. a cam member if the sliding part is a rocker arm).